New physics effects in tree-level decays

Abstract

We critically review the assumption that no new physics is acting in tree-level $B$-meson decays and study the consequences for the ultimate precision in the direct determination of the CKM angle $\gamma$. In our exploratory study we find that sizable universal new physics contributions, $\Delta C_{1,2}$, to the tree-level Wilson coefficients $C_{1,2}$ of the effective Hamiltonian describing weak decays of the $b$ quark are currently not excluded by experimental data. In particular we find that Im $\Delta C_1$ and Im $\Delta C_2$ can easily be of order $\pm 10$ without violating any constraints from data. Such a size of new physics effects in $C_1$ and $C_2$ corresponds to an intrinsic uncertainty in the CKM angle $\gamma$ of the order of $|\delta \gamma |\approx 4^{\circ }$, which is slightly below the current experimental precision. The accuracy in the determination of $\gamma$ can be improved by putting stronger constraints on the tree-level Wilson coefficients, in particular $C_1$. To this end we suggest a more refined theoretical study as well as a more precise measurements of the observables that currently provide the strongest bounds on hypothetical new weak phases in $C_1$ and $C_2$. We note that the semi-leptonic CP asymmetries seem to have the best prospect for improving the bound on the weak phase in $C_1$.

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• Standard Model Predictions for Rare K and B Decays without New Physics Infection
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• The time-dependent angular analysis of $B_d\to K_S\ell \ell$, a new benchmark for new physics
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• New Physics in $B_q^0-{\bar{B}}_q^0$ Mixing: Present Challenges, Prospects, and Implications for $B_q^0\to {\mu }^{+}{\mu }^{-}$
• Observation of the decay $B_s^0\to {\bar{D}}^0\varphi$
• Observation of the decay $B_s^0\to {\overline{D}}^0{K}^{+}{K}^{-}$
• Model-independent measurement of the CKM angle $\gamma$ using $B^0\to D{K}^{\ast 0}$ decays with $D\to K_S^0{\pi }^{+}{\pi }^{-}$ and $K_S^0{K}^{+}{K}^{-}$
• Observation of $B_s^0\to {\overline{D}}^{\ast 0}\varphi$ and search for $B^0\to {\overline{D}}^0\varphi$ decays
• Using $B_s^0\to D_s^{\mp }{K}^{\pm }$ Decays as a Portal to New Physics
• Revealing New Physics in $B_s^0\to D_s^{\mp }{K}^{\pm }$ Decays
• The history of LHCb
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• Electroweak effects in the extraction of the CKM angle $\gamma$ from $B\to D\pi$ decays
• On the impact of meson mixing on $B_s\to \varphi ee$ angular observables at low $q^2$
• Probing new physics in class-I $B$-meson decays into heavy-light final states
• HQET sum rules for matrix elements of dimension-six four-quark operators for meson lifetimes within and beyond the Standard Model
• Measurement of $CP$ asymmetries and branching-fraction ratios for $B^{\pm }\to D{K}^{\pm }$ and $D{\pi }^{\pm }$ with $D\to K_{\mathrm{S}}^0{K}^{\pm }{\pi }^{\mp }$ using Belle and Belle II data
• $B_s^0$-${\bar{B}}_s^0$ Oscillations as a New Tool to Explore CP Violation in $D_s^{\pm }$ Decays
• A model-independent measurement of the CKM angle $\gamma$ in the decays $B^{\pm }\to [K^{+}{K}^{-}{\pi }^{+}{\pi }^{-}{]}_D{h}^{\pm }$ and $B^{\pm }\to [{\pi }^{+}{\pi }^{-}{\pi }^{+}{\pi }^{-}{]}_D{h}^{\pm }$ ($h=K,\pi$)
• Theory Motivation: What measurements are needed?
• A model-independent measurement of the CKM angle $\gamma$ in partially reconstructed $B^{\pm }\to D^{\ast }{h}^{\pm }$ decays with $D\to K_S^0{h}^{+}{h}^{-}$ $(h=\pi ,K)$
• CP violation measurements in b hadrons at LHCb